What is "dense" in DensePose?
In computer vision, the adjectives dense and sparse are used in a variety of tasks (e.g. optimal flow), but they are commonly used in the context of the correspondence problem, which is the problem of finding a map (or correspondence) between pixels of two images (e.g. two successive frames of a video). In this context, these adjectives thus refer to the number of pixels of the image that are used to solve this specific task. A dense correspondence is thus a correspondence between two images using all (or, at least, many) pixels. In other words, a dense correspondence attempts to map all (or many) pixels of an image to all (or many) pixels of another image.

In the case of DensePose, the correspondences are between RGB images and surface-based representation of the human body (the figures of the paper illustrates this).